The is the multiple category search addon I offer those who request it that have purchase either the Extension Pro pack of the Pro Pack. It is supplied as is function and/style though I can provide CSS to change the accent color. This addon can be difficult to configure because it is setup via a shortcode many options. probably the most difficult is the category option to search by multiple categories.

The page linked to, they did tweak the styles slightly, primarily the three column layout. The layout is stacked.

If you are interested in this addon, I see you have purchased a couple addons already, I can work with you in order to offer an “upgrade pricing” to the Extension Pro Pack. Let me know.